Vacuum pumping for mercury rectifiers



June 2l, 1938. *i i L, A. KILGoRE ET AL ,2,121,599

VACUUM vPUMPIICT FOR MERCURY vREKJTIIFIIEIRS ATTORNEY June 21 1938- A, KILGORE ET AL 2,121,599.

VACUUM FUMPING FOR MERCURY RECTIFIERS 1 Filed Sept. 3, 1957 2 Sheets-Sheet 2 INVENTORS.

' ATTORNY Patented June 21, 1938 VACUUM PUMPING F entrar orrice OR MERCURY RECTI- ERS Lee A. Kilgore and Joseph H. Cox, assignors to Westinghouse Forest Hills, Electric a Manufacturing Company, East Pittsburgh, Pa., a corporation of `Pennsylvania Application September 3, 1937, Serial No. 162,300

Claims.

Our invention relates to vacuum pumps and ithas particular relation to improvements in the transfer of mercury between the pump and a mercury arc rectifier.

In evacuating mercury arc rectifers by means ofniercury vapor vacuum pumps, considerable difficulty has been experienced in maintaining the quantity of mercury in the mercuryfboiler more or less constant. In the operation oi the rectier, mercury vapor diii'uses back and forth between the vapor pump and the rectiiier. Difficulty has been experienced in not having enough aswell as having an excess amount of mercury enter'vrthe vacuum pump. By our larrangement we'gain a further advantage by insuring a contnuous iiow'of mercury in'one direction. With certain designs the quantity of mercury in the mercury boiler varies from 25% to 200% of the normal amount necessary for stable operation. When the lower limit is reachedjthere is the danger of overheating the boiler randproducing scale, which consequently reduces the life of the boiler. On the other hand, when the upper limit is reached, it was necessary to periodically detach the pump from the converter and remove the surplus mercury. Prior art systems of this character of which we are fully aware confine the position of the vacuum pump with respect to the rectifier so that the pump unit must be stationed considerably higher than the rectifier unit to insure a now of the excess mercury above the quantity normally required in the pump boiler to the container of the rectifier. Likewise, such systems require a connection to the container of the rectier, usually through the water jacket. Such an arrangement is not only expensive and undesirable from the standpoint that a special valve is required for the connection that conducts excess mercury, but it is inconvenient to service. Ordinarily, the pump must be cleaned about once a year due to the accumulation of oxides on the interior metal surfaces. To service pumps contained partly within the container of the rectiiier is disadvantageous in that the vacuum in the rectier is broken upon removal of the pump unit. f

This limitation, which has been the chief source of diiiculty in maintaining stability of operation is eliminated, in the construction according to our invention. In accordance with our invention, we provide an arrangement whereby excess mercury flows in the direction of the pump. The surplus mercury accumulating in the boiler is returned to the rectier by connecting a conduit between the mercury boiler producing the op- (Cl. Z50-27.5)

erating vapor for the pump and an auxiliary mercury boiler.

By...placing our auxiliary Aboiler in a position so Qthatthe'bottom is at the samerlevel as the surface oi the mercury contained in the principal boiler, the excess is vaporized.A A conduit connected between the auxiliary boiler and the rectiiler conducts the mercury vapor ,towards the evacuated tank. At the entrance tothe tank, an inverted conduit, surrounded by a cooling agent, preferably natural water, condenses the mercury vapor on its downward path and causes it to return to the rectifier so that the cathode therein is continually and automatically restored. By our arrangement, the pumping unit may be stationed at any convenient location adjacent the rectifier unit for the flow of excess mercury from the pump boiler to the rectiiier container is independent of the relative position of the several units. Likewise, in servicing our pumps, the vacuum .in the rectifier need not be disturbed for by simply closing the main tank valve, the pump can be detached and cleaned or a reserve pump may be quickly attached without any serious delay in rectier service.

It is an object of our invention to provide a system for maintaining the mercury in a mercury vapor pump at the desired level for satisfactory operation. y

It is another object of our invention to provide an auxiliary boiler to dispose of the excess mercury accumulating in the pumping system, thereby eliminating the necessity for periodically servicing the pumps to control the amount of mercury therein.

A still further object of our invention is to provide a pumping system that will result in more stable operation of the recticr by lessening the possibilities of faulty operation.

A still further object of our invention is to maintain the quantity of mercury in the cathode oi the rectier constant.

Other objects and advantages of our invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

Figure l is a sectional View of our improved pumping system showing the auxiliary boiler and the necessary conduits according to our invention; and,

Fig. 2-is a sectional view similar to Fig. 1 showing a modification thereof.

In the illustrative embodiment of our invention according to Fig. l, Ya section of a mercuryarc rectifier 3, is shown comprising a tank 5 and Wherefrom mercury is continually boiled 01T during operation. In exhausting the rectifier 3, a continuous stream of mercury Vapor diffuses between the pump 9 and the rectifier 3 with other' gases and enters or leaves the pump 9 through the exhaust tube 1.

In the operation of a vacuum pump 9, an electric heater I3 located in the base of the pump 9 supplies heat to the mercury boiler I5. A blast of mercury vapor from the boiler I passesrup through a funnel-shaped tube I1 and is directed downwards and outwards against a water cooled surface of the pump 9 at an angle after striking a deflector 2i. The vapor is condensed on the cooled wall I9 and the liquid mercury falls down along the pump barrel 23 and ows back to the boiler I5. Any gas leaving the rectier 3 through the exhaust tube diffuses into the vapor stream and is carried along with it.

Cooling coils 25 wound around the pump barrel 23 form an efficient cooling system. A roughing pump (not shown) connected to an exhaust tube 21 discharges the pumped gases to atmosphere.

It will be seen that, according to our arrangement, the mercury boiler I5 is gradually accumulating mercury from the rectifier 3. An auxiliary mercury boiler 29 connected with the principal boiler I5 by a conduit 3l is so positioned that mercury accumulating in the boiler I5 above a predetermined quantity flows to the auxiliary boiler 23. Conduit 3i is connected to the principal boiler I5 at a point below the surface of the mercury contained therein and to the base of the auxiliary boiler 29.

Our auxiliary boiler 29 may be heated by a p separate electrical heater 33 or as shown in Fig.

2, it may obtain its heat from the principal heater I3. Caution must be taken not to overheat the auxiliary boiler 29, since it will contain very little mercury during a greater part of the time while the pumpY 9 is in operation. Any mercury transferred to the auxiliary boiler 29 is vaporized and rises in the conduit 31 connecting the auxiliary boiler 29 and another inverted conduit 39, surrounded by a cooling device, preferably cooling coils 4I containing water. The inverted conduit 39 is preferably attached to the exhaust tube 1 connecting the rectifier 3 and the pump 9 at a point such that the condensed mercury fiows towards the rectier 3. The evaporated mercury condenses on its downward path in the inverted conduit 39 and in the conduit 1 so that the liquid mercury returns to the cathode I I of the rectifier 3. Valves 43 inserted between the mercury vapor pump 9 and the rectifier tank 5 are closed permitting detachment of the pump unit 9 from the rectifier 3 when an inspection of the pump 9 is necessary.

As shown in Fig. 2, the arrangement provides a mercury trap 45 with a sloping conduit 41 connecting the rectier 3 with the trap 45 and another sloping conduit 49 connecting the pump 9 and the trap 45. The length of these conduits 41 and 49 are so proportioned as to maintain a -continuous ow of mercury vapor into the pump. A lagging 35 completely surrounds the boiler I5 and the auxiliary boiler 29 in order to maintain enough heat within the auxiliary boiler 29. The operation of the apparatus is essentially as described in connection with the embodiment of the invention in Fig. 1.

While we have shown and described a preferred embodiment of our invention, it is apparent that changes and modifications may be made therein without departing from the spirit and scope of our invention. We desire, therefore, that only such limitations be imposed as are embodied in the accompanying claims or as may be necessitated by the prior art.

We claim as our invention:

1. The combination with an evacuated vessel of a vacuum pumping system comprising a vapor pump, an auxiliary evaporating means, a conduit connected between said pump and said auxiliary evaporating means, a vaporizable medium in said pump and overflowing into said auxiliary evaporating means and a connection from said auxiliary evaporating means for returning the evaporated vaporizable medium to the evacuated vessel.

2. The combination with a vacuum vessel of a vacuum pumping device comprising a vapor pump, an auxiliary vaporizing means, a conduit connecting said pump and said auxiliary vaporizing means, a vaporizable medium in said pump, said auxiliary vaporizing means being so positioned as to maintain the vaporizable medium at a predetermined level in said pump and means for delivering the vaporizable medium evaporated by said auxiliary evaporating means to the vacuum vessel.

3. The combination with a receptacle to be evacuated of a vacuum pumping device comprising a vapor pump, a vaporizable pumping ud in said pump, means for receiving any Vaporizable pumping iiuid in excess of the quantity desired in said pump, means for evaporating the excess fluid in said receiving means, means for condensing the fluid evaporated by said means, said condensing means being so positioned that the condensed fluid is returned to the receptacle to be evacuated.

4. The combination with a mercury arc converter of a pumping system comprising a mercury vapor pump for said converter, a connection between said pump and said converter, said connection being so arranged that during operation of the converter, mercury vapor will flow from said converter into said pump, a mercury boiler for supplying operating vapor to said pump, an auxiliary boiler, a conduit connecting said boiler and said auxiliary boiler and a conduit extending from said auxiliary boiler to said connection.

5. The combination with a mercury arc converter of an evacuating system comprising a mercury vapor pump for said converter, a connection between said pump and said converter, said connection being so arranged that during normal operation of the converter, mercury vapor will flow from said converter into said pump, a mercury boiler for supplying operating vapor to said pump, an auxiliary boiler, a conduit connecting said boiler and said auxiliary boiler, a conduit extending from said auxiliary boiler to said connection, and means for sealing said connection so that said pump and said auxiliary boiler may be removed asa unit from said converter.

6. The combination with an evacuated vessel of a vacuum pumping system comprising a vapor pump, an auxiliary evaporating means, a conduit connecting saidY pump and said evaporating means, a condensing means including a conduit connecting said vaporizing means and said condensing means, and a valve system so situated with respect to said pump and said auxiliary means and the said evacuated vessel as to make the said evacuated vessel detachable from said pumping system.

'7. The combination with an evacuated vessel of a vacuum pumping system comprising a vapor pump, a vaporizable pumping iluid in said pump, a mercury trapping means, a conduit connecting said trapping means and saidv evacuated vessel, said conduit sloping towards said evacuated vessel, a conduit between said trapping means and said pump, said conduit sloping towards said pump, and the said conduits so proportioned as to permit a continuous flow of mercury vapor to enter said pump from said evacuated vessel, and means for returning surplus vaporizable material from said pump to said evacuated vessel.

8. In combination with a mercury arc converter, an evacuating system comprising a mercury vapor pump, a mercury boiler for supplying operating vapor to said pump, a connection from said pump to said converter, said connection being cooled to condense the greater portion of the vapor entering said connection, a

portion of said connection adjacent said con verter being inclined so that mercury condensed therein returns to said vapor device, a further portion of said connection being so arranged that mercury condensed therein ows into the pump, an auxiliary boiler, a conduit connecting said pump boiler with said auxiliary boiler whereby surplus mercury flows from said pump boiler to said auxiliary boiler and means for conducting vapor from said auxiliary boiler to that portion of the connection wherein condensed mercury returns to the vapor device.

9. In combination with a mercury arc converter, an evacuating system comprising a mercury vapor pump, a mercury boiler for supplying operating vapor to said pump, a, connection from said pump to said converter, said connection being cooled to condense the greater portion of the vapor entering said connection, a portion of said connection `adjacent said converter being inclined so that mercury condensed therein returns to said vapor device, a further portion of said connection being so arranged that mercury condensed therein flows into the pump, an auxiliary boiler, a conduit connecting said pump boiler with said auxiliary boiler whereby surplus mercury flows from saidpump boiler to said auxiliary boil'er and means for conducting vapor from said auxiliary boiler to that portion of the connection wherein condensed mercury returns to the vapor device, and Valve means for sealing said device so that the evacuating system can be opened without disturbing the vacuum in the device.

10. In combination with a mercury-arc device, a pumping system comprising a mercury vapor pump, connecting means for connecting said pump to said device, said connection being so arranged that during operation of the device mercury vapor diffuses into said pump, means .for receiving excess mercury received in said pump, a means for vaporizing said excess mercury and means for returning the vaporized excess mercury to the mercury-arc device.

LEE A. KILGORE. JosEPH H. cox. 

